As regular visitors to this forum may have noticed I have been experimenting with using the CGY750 governor on a 500ESP, as reported HERE.

This first involved fitting magnets to the autorotation gear, and then to the main gear, using the supplied hall effect sensor. Whilst reasonably good results were obtained, I felt that a phase sensor was more appropriate for an electric heli, and couldn't resist the temptation to give that a try. Ultimately the results have been worthwhile as reported below.

Before continuing though I'd like to thank ollie2893 and Dr.Ben in particular for their input and enthusiasm.

V-BAR user have reported some success with the Hyperion Phase Sensor which is very cheap. It seemed the obvious basis for the project, available HERE in the US, and HERE in the UK for under a very modest sum.

Upon arrival mine looked thus:

And out of the packet:

And, heatshrink removed:

Unfortunately the output pulse rate from the phase sensor is too high for the CGY750. Using a 14T pinion with a 162T main gear, and with the sensor giving 3 pulses per revolution of the motor, the motor-pulse:head-speed ratio is 34.71, higher than the 30.00 max of the CGY750 governor. It was therefore necessary to pre-scale these pulses. Dividing by two would allow a ratio of 17.36:1. The Rsen connection to the CGY750 provides a regulated 3V output, so any circuitry attached to it, unless sourcing power from elsewhere, needs to be able to operate at this voltage. Fortunately the 74HC logic family operates on 2 to 6V. In order to pre-scale the signal by 2, 4, or 8 times I selected a 74HC93 device as shown below:

As can be seen this consists of a 1 stage and 3 stage ripple counter. I chose to use only the 3 bit counter as this would give me the flexibility in output pulse rate I sought.

As can be seen below, the phase sensor fortunately has no components on the rear.

I was therefore able to mount the 74HC93 on the rear of the board without obstruction. To mount it I removed the solder resist from the ground plane adjacent to where pins 2, 3, 6, 7, 13 and 14 would sit. This provided for secure mounting of the device using n/c pins, and unused inputs which needed to be grounded. The board was then tinned:

And with all other pins straightened so eliminate any shorting to the ground plane, the device mounted:

I then superglued an 0805 2K7 resistor to the top of the chip and wired the output signal from the phase sensor to one end of the resistor and on to pin 1, the input to the 3 bit counter section. I also fitted a 1210 0.1uF decoupler cap across the 0V/3V connections and ran the 3V line to the other end of the resistor and on to pin 5, the power input.

Next I added a ground wire to pin 10, which was too close to the single (3V) track on the back of the PCB to simply connect it to the ground plane.

I also connected the output of the divide by two stage of the counter (pin 9) to the output lead. NOTE THAT THIS SUBSEQUENTLY WAS MOVED to pin 8, see below.

For those who find battery connections hard to solder, see below the modified board next to a servo connector for scale!

I then potted both sides of the board in epoxy to protect the wiring:

Installation was simple. The red sense wire was connected to one of the ESC leads to the motor:

The sense wire was run, protected by braiding, past the motor to the phase sensor, now enclosed in heatshrink and cable-tied to the inside of the frame at the top of the 'X':

And the output cable was then run into the Rsen input of the CGY750.

Alas first results were not good! The RPM display on the CGY750 peaked at 2091 rpm and refused to read any higher. I checked the signal of an oscilloscope and it looked perfect, a 50:50 duty cycle square wave, but clearly the CGY750 didn't like it. The supplied hall effect sensor waveform is a sequence of relatively short positive spikes, so for a given frequency the low period of the input signal to the CGY750 would be much longer. Also considering that I'm running at the top end of the RPM range (2720rpm), I figured that this low period was perhaps too short, output from my divide by two counter. I therefore removed the heatshrink and drilled into the epoxy to move the output wire from pin 9 to pin 8, turning the pre-scaler into a divide by four.

Changing the gear ratio from 17.36 to 8.68, the CGY750 was then happy over the full RPM range. Initial testing was hampered by me leaving the LLmt_Hov and LLmtIdup gov advanced settings too high, so the gov wouldn't regulate at a low speed. I checked the headspeed using a laser tacho and this agreed with that shown on the CGY750 display.

On to the flight tests and I found that the tail wagged and gov hunted. Most disappointing. I tried Quick/Middle/Moderate settings etc to no avail. I then checked the gov basic menu and found that the servo type was set to analog, not DG:1520. Changing that made all the difference, and suddenly everything started working as hoped/expected.

At takeoff with a full battery there's a little hunting lasting maybe 5s and then the flight was perfect. Punch-outs had no audible dip in head-speed, nor fluttering.

I've only had one proper flight before it started to rain, but I believe the slight hunting at the start of the flight is probably due to the Rv.DnDly being too low, my reasoning being that this governor is designed for use with IC engines which have engine braking. Unless I turn on the braking function in the ESC, the electric motor is unbraked and so won't respond very quickly to a reduction in throttle input. A large Rv.DnDly should go some way to address this. I'll report back.

No, the 74HC93 is a binary counter, so it can divide by 2, 4, 8 or 16. For a 10 pole motor you'd get 5 pulses per revolution, which probably wouldn't work at the same head-speed (2720) using divide by four, but you could wire up the output to pin 11 to get divide by eight. Of course this all depends on your gearing and head-speed.

A quick bit of hovering in the garden with a couple of fully charged batteries has led me to the following settings:

Rv.UpDly: 14Frm
Rv.DnDly: 18Frm

There's a very slight hunt on takeoff, but this very quickly vanishes.

Hoping for a better fly at the park tomorrow lunchtime.

Incidentally, note that the Maximum RPM display on the CGY750 gets somewhat confused by the startup beeps from the ESC, so if you want to use that, be sure to reset it after poweron. For the record I see an overspeed to about 2810rpm before the head-speed settles down to the desired 2720.

I have completed three of these. I am really want to test this.. If anyone else wants one and can't build your own I will sell two of them. I don't want to make any more right now. Don't let the pictures fool you these parts are tiny.

I plugged in a new, unmodified phase sensor, initially leaving the gear ratio at 8.68 where it had been with my divide by 4 pre-scaler. On the bench, blades removed, I span up the heli (500ESP) and the rpm display on the CGY750 went up to 4602rpm. I then set the ratio to 34.71 which is where it should be without pre-scaling (3*162/14). The rpm reading then hit a limit of 1134rpm, rather less than the required 2700 or so. Admittedly I didn't have a pull-up fitted, and I didn't have my oscilloscope to hand to see if one would be needed, but the simple response is that, unmodified, this doesn't work with firmware 1.2.

I've not had much chance to fly since October, but I've recently tried to get the gov working properly with 1.2 and my converted phase sensor and failed to get a solid lock. In the end I switched the gov off on the Tx, which still left the gov enabled on the CGY750 for the purpose of reading the current head-speed from the sensor. This gave the piro compensation the head speed info it needed. Flew very well, albeit with a slight drop in head speed towards the end of the flight.